Things You'll Need
Coin or jewelry cleaning solution
Rag or soft toothbrush
When exposed to water for prolonged periods of time, a variety of issues can cause coins to become dirty, grimy and even green. When copper is exposed to the elements for prolonged periods of time it can develop a green patina. Algae and hard-water scale can also affect coins in these ways. A variety of methods can be used to clean up your coins. The time and effort involved may depend on the severity of the grime and damage.
Consider whether you should clean your coins. If you are dealing with rare, collectible coins you should probably avoid cleaning them, no matter the appearance. If collectible coins absolutely must be washed, you should take them to a professional dealer who can do the job with a minimal amount of damage to the coin. If, however, you are dealing with common coins in circulation that need to cleaned up so they don't spread grime inside your wallet or pocket, you can use the following steps.
Soak the coins in a solution of Clorox and water. Follow this with a rinse in a container of hot water mixed with a little dish detergent. Lastly, rinse the coins in cold, clean water. This should remove any algae from the coins. If your coins still look dirty, move on to the next step.
Soak the coins in white vinegar and rinse with cool, clean water. This should remove any hard-water stains. If your coins still look a bit green, move on to the next step.
To remove the green patina that can develop on copper, soak your coins in a solution of baking soda and water. You may need to scrub lightly with a soft toothbrush or rag.
For very persistent stains, use a professional coin or jewelry cleaning solution and follow the instructions on the bottle.
Though pennies will develop the worst patina from their exposure to flood waters, remember that other coins have a copper core that shows enough to cause them to develop this patina, as well.
Never apply these harsh cleaning methods to collectible coins. Visit the resources section for advice on dealing with dirty collectibles.